Method and apparatus for bilayer photoresist dry development

ABSTRACT

A method for etching an organic anti-reflective coating (ARC) layer on a substrate in a plasma processing system comprising: introducing a process gas comprising nitrogen (N), hydrogen (H), and oxygen (O); forming a plasma from the process gas; and exposing the substrate to the plasma. The process gas can, for example, constitute an NH 3 /O 2 , N 2 /H 2 /O 2 , N 2 /H 2 /CO, NH 3 /CO, or NH 3 /CO/O 2  based chemistry. Additionally, the process chemistry can further comprise the addition of helium. The present invention further presents a method for forming a bilayer mask for etching a thin film on a substrate, wherein the method comprises: forming the thin film on the substrate; forming an ARC layer on the thin film; forming a photoresist pattern on the ARC layer; and transferring the photoresist pattern to the ARC layer with an etch process using a process gas comprising nitrogen (N), hydrogen (H), and oxygen (O).

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims the benefit of U.S. ProvisionalApplication No. 60/435,286, which was filed on Dec. 23, 2002, U.S.Provisional Application No. 60/483,235, which was filed on Jun. 30,2003, and U.S. Provisional Application No. 60/483,234, which was filedon Jun. 30, 2003; the contents of which are hereby incorporated in theirentirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for plasmaprocessing a substrate, and more particularly to a method for bilayerphotoresist dry development.

BACKGROUND OF THE INVENTION

During semiconductor processing, a (dry) plasma etch process can beutilized to remove or etch material along fine lines or within vias orcontacts patterned on a silicon substrate. The plasma etch processgenerally involves positioning a semiconductor substrate with anoverlying patterned, protective layer, for example a photoresist layer,in a processing chamber. Once the substrate is positioned within thechamber, an ionizable, dissociative gas mixture is introduced within thechamber at a pre-specified flow rate, while a vacuum pump is throttledto achieve an ambient process pressure. Thereafter, a plasma is formedwhen a fraction of the gas species present are ionized by electronsheated via the transfer of radio frequency (RF) power either inductivelyor capacitively, or microwave power using, for example, electroncyclotron resonance (ECR). Moreover, the heated electrons serve todissociate some species of the ambient gas species and create reactantspecie(s) suitable for the exposed surface etch chemistry. Once theplasma is formed, selected surfaces of the substrate are etched by theplasma. The process is adjusted to achieve appropriate conditions,including an appropriate concentration of desirable reactant and ionpopulations to etch various features (e.g., trenches, vias, contacts,etc.) in the selected regions of the substrate. Such substrate materialswhere etching is required include silicon dioxide (SiO₂), low-kdielectric materials, poly-silicon, and silicon nitride.

SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus for plasmaprocessing a substrate, and to a method and apparatus for bilayerphotoresist dry development.

In one aspect of the invention, a method and apparatus are described foretching an anti-reflective coating (ARC) layer on a substrate in aplasma processing system. A process gas comprising one or more gassescollectively containing nitrogen (N), hydrogen (H), and oxygen (O) isintroduced. A plasma is formed from the process gas in the plasmaprocessing system. The substrate is exposed to the plasma.

Additionally, a method and apparatus are described for forming a bilayermask for etching a thin film on a substrate. The thin film is formed onthe substrate. An anti-reflective coating (ARC) layer is formed on thethin film. A photoresist pattern is formed on the ARC layer. Thephotoresist pattern is transferred to the ARC layer by etching the ARClayer using a process gas comprising one or more gasses collectivelycontaining nitrogen (N), hydrogen (H), and oxygen (O).

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A, 1B, and 1C show a schematic representation of a typicalprocedure for pattern etching a thin film;

FIG. 2 shows a simplified schematic diagram of a plasma processingsystem according to an embodiment of the present invention;

FIG. 3 shows a schematic diagram of a plasma processing system accordingto another embodiment of the present invention;

FIG. 4 shows a schematic diagram of a plasma processing system accordingto another embodiment of the present invention;

FIG. 5 shows a schematic diagram of a plasma processing system accordingto another embodiment of the present invention;

FIG. 6 shows a schematic diagram of a plasma processing system accordingto another embodiment of the present invention;

FIG. 7 presents a method of etching an anti-reflective coating (ARC)layer on a substrate in a plasma processing system according to anembodiment of the present invention; and

FIG. 8 presents a method of forming a bilayer mask for etching a thinfilm on a substrate according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

In material processing methodologies, pattern etching comprises theapplication of a thin layer of light-sensitive material, such asphotoresist, to an upper surface of a substrate, that is subsequentlypatterned in order to provide a mask for transferring this pattern tothe underlying thin film during etching. The patterning of thelight-sensitive material generally involves exposure by a radiationsource through a reticle (and associated optics) of the light-sensitivematerial using, for example, a micro-lithography system, followed by theremoval of the irradiated regions of the light-sensitive material (as inthe case of positive photoresist), or non-irradiated regions (as in thecase of negative resist) using a developing solvent. Multi-layer maskscan be implemented for etching features in a thin film. For example, asshown in FIGS. 1A-C, a bilayer mask 6 comprising light-sensitive layer 3with pattern 2 formed using conventional lithographic techniques and anorganic anti-reflective coating (ARC) layer 7 can be utilized as a maskfor etching the thin film 4, wherein the mask pattern 2 in thelight-sensitive layer 3 is transferred to the ARC layer 7 using aseparate etch step preceding the main etch step for the thin film 4.

In one embodiment, a process gas comprising a nitrogen (N) containinggas, a hydrogen (H) containing gas, and an oxygen (O) containing gas isutilized as a method of bilayer photoresist dry development.Alternatively, two or more of nitrogen (N), hydrogen (H), and oxygen (O)can be included in a single gas. For example, an ammonia-oxygen (NH₃/O₂)based chemistry can be introduced as a method of bilayer photoresist drydevelopment. In an alternate embodiment, a nitrogen-hydrogen-oxygen(N₂/H₂/O₂) based chemistry can be employed to facilitate etching theorganic ARC layer. Alternately, carbon monoxide (CO) can be added, orutilized to replace O₂ in the former two chemistries. Alternately, theprocess gas can comprise ammonia (NH₃), carbon monoxide (CO), and oxygen(O₂). Alternately, the process gas can further comprise helium (He).Such chemistries can be employed to create high aspect ratio featureshaving an aspect ratio greater than or equal to about 3-to-1, or evengreater than or equal to about 4-to-1.

According to one embodiment, a plasma processing system 1 is depicted inFIG. 2 comprising a plasma processing chamber 10, a diagnostic system 12coupled to the plasma processing chamber 10, and a controller 14 coupledto the diagnostic system 12 and the plasma processing chamber 10. Thecontroller 14 is configured to execute a process recipe comprising atleast one of the above-identified chemistries (i.e. NH₃/O₂, N₂/H₂/O₂,NH₃/CO, N₂/H₂/CO, NH₃/O₂/CO, etc.) to etch an organic ARC layer.Additionally, controller 14 is configured to receive at least oneendpoint signal from the diagnostic system 12 and to post-process the atleast one endpoint signal in order to accurately determine an endpointfor the process. In the illustrated embodiment, plasma processing system1, depicted in FIG. 2, utilizes a plasma for material processing. Plasmaprocessing system 1 can comprise an etch chamber.

According to the embodiment depicted in FIG. 3, plasma processing system1 a can comprise plasma processing chamber 10, substrate holder 20, uponwhich a substrate 25 to be processed is affixed, and vacuum pumpingsystem 30. Substrate 25 can be, for example, a semiconductor substrate,a wafer or a liquid crystal display. Plasma processing chamber 10 canbe, for example, configured to facilitate the generation of plasma inprocessing region 15 adjacent a surface of substrate 25. An ionizablegas or mixture of gases is introduced via a gas injection system (notshown) and the process pressure is adjusted. For example, a controlmechanism (not shown) can be used to throttle the vacuum pumping system30. Plasma can be utilized to create materials specific to apre-determined materials process, and/or to aid the removal of materialfrom the exposed surfaces of substrate 25. The plasma processing system1 a can be configured to process 200 mm substrates, 300 mm substrates,or substrates of any size.

Substrate 25 can be, for example, affixed to the substrate holder 20 viaan electrostatic clamping system. Furthermore, substrate holder 20 can,for example, further include a cooling system including a re-circulatingcoolant flow that receives heat from substrate holder 20 and transfersheat to a heat exchanger system (not shown), or when heating, transfersheat from the heat exchanger system. Moreover, gas can, for example, bedelivered to the back-side of substrate 25 via a backside gas system toimprove the gas-gap thermal conductance between substrate 25 andsubstrate holder 20. Such a system can be utilized when temperaturecontrol of the substrate is required at elevated or reducedtemperatures. For example, the backside gas system can comprise atwo-zone gas distribution system, wherein the helium gas gap pressurecan be independently varied between the center and the edge of substrate25. In other embodiments, heating/cooling elements, such as resistiveheating elements, or thermo-electric heaters/coolers can be included inthe substrate holder 20, as well as the chamber wall of the plasmaprocessing chamber 10 and any other component within the plasmaprocessing system 1 a.

In the embodiment shown in FIG. 3, substrate holder 20 can comprise anelectrode through which RF power is coupled to the processing plasma inprocess space 15. For example, substrate holder 20 can be electricallybiased at a RF voltage via the transmission of RF power from a RFgenerator 40 through an impedance match network 50 to substrate holder20. The RF bias can serve to heat electrons to form and maintain plasma.In this configuration, the system can operate as a reactive ion etch(RIE) reactor, wherein the chamber and an upper gas injection electrodeserve as ground surfaces. A typical frequency for the RF bias can rangefrom about 0.1 MHz to about 100 MHz. RF systems for plasma processingare well known to those skilled in the art.

Alternately, RF power is applied to the substrate holder electrode atmultiple frequencies. Furthermore, impedance match network 50 serves toimprove the transfer of RF power to plasma in plasma processing chamber10 by reducing the reflected power. Match network topologies (e.g.L-type, π-type, T-type, etc.) and automatic control methods are wellknown to those skilled in the art.

Vacuum pump system 30 can, for example, include a turbo-molecular vacuumpump (TMP) capable of a pumping speed up to 5000 liters per second (andgreater) and a gate valve for throttling the chamber pressure. Inconventional plasma processing devices utilized for dry plasma etch, a1000 to 3000 liter per second TMP is generally employed. TMPs are usefulfor low pressure processing, typically less than 50 mTorr. For highpressure processing (i.e., greater than about 100 mTorr), a mechanicalbooster pump and dry roughing pump can be used. Furthermore, a devicefor monitoring chamber pressure (not shown) can be coupled to the plasmaprocessing chamber 10. The pressure measuring device can be, forexample, a Type 628B Baratron absolute capacitance manometercommercially available from MKS Instruments, Inc. (Andover, Mass.).

Controller 14 comprises a microprocessor, memory, and a digital I/O portcapable of generating control voltages sufficient to communicate andactivate inputs to plasma processing system 1 a as well as monitoroutputs from plasma processing system 1 a. Moreover, controller 14 canbe coupled to and can exchange information with RF generator 40,impedance match network 50, the gas injection system (not shown), vacuumpump system 30, as well as the backside gas delivery system (not shown),the substrate/substrate holder temperature measurement system (notshown), and/or the electrostatic clamping system (not shown). Forexample, a program stored in the memory can be utilized to activate theinputs to the aforementioned components of plasma processing system 1 aaccording to a process recipe in order to perform the method of etchingan organic ARC layer. One example of controller 14 is a DELL PRECISIONWORKSTATION 610™, available from Dell Corporation, Austin, Tex.

The diagnostic system 12 can include an optical diagnostic subsystem(not shown). The optical diagnostic subsystem can comprise a detectorsuch as a (silicon) photodiode or a photomultiplier tube (PMT) formeasuring the light intensity emitted from the plasma. The diagnosticsystem 12 can further include an optical filter such as a narrow-bandinterference filter. In an alternate embodiment, the diagnostic system12 can include at least one of a line CCD (charge coupled device), a CID(charge injection device) array, and a light dispersing device such as agrating or a prism. Additionally, diagnostic system 12 can include amonochromator (e.g., grating/detector system) for measuring light at agiven wavelength, or a spectrometer (e.g., with a rotating grating) formeasuring the light spectrum such as, for example, the device describedin U.S. Pat. No. 5,888,337.

The diagnostic system 12 can include a high resolution Optical EmissionSpectroscopy (OES) sensor such as from Peak Sensor Systems, or VerityInstruments, Inc. Such an OES sensor has a broad spectrum that spans theultraviolet (UV), visible (VIS), and near infrared (NIR) lightspectrums. The resolution is approximately 1.4 Angstroms, that is, thesensor is capable of collecting 5550 wavelengths from 240 to 1000 nm.For example, the OES sensor can be equipped with high sensitivityminiature fiber optic UV-VIS-NIR spectrometers which are, in turn,integrated with 2048 pixel linear CCD arrays.

The spectrometers receive light transmitted through single and bundledoptical fibers, where the light output from the optical fibers isdispersed across the line CCD array using a fixed grating. Similar tothe configuration described above, light emitting through an opticalvacuum window is focused onto the input end of the optical fibers via aconvex spherical lens. Three spectrometers, each specifically tuned fora given spectral range (UV, VIS and NIR), form a sensor for a processchamber. Each spectrometer includes an independent A/D converter. Andlastly, depending upon the sensor utilization, a full emission spectrumcan be recorded every 0.1 to 1.0 seconds.

In the embodiment shown in FIG. 4, the plasma processing system 1 b can,for example, be similar to the embodiment of FIG. 2 or 3 and furthercomprise either a stationary, or mechanically or electrically rotatingmagnetic field system 60, in order to potentially increase plasmadensity and/or improve plasma processing uniformity, in addition tothose components described with reference to FIG. 2 and FIG. 3.Moreover, controller 14 can be coupled to magnetic field system 60 inorder to regulate the speed of rotation and field strength. The designand implementation of a rotating magnetic field is well known to thoseskilled in the art.

In the embodiment shown in FIG. 5, the plasma processing system 1 c can,for example, be similar to the embodiment of FIG. 2 or FIG. 3, and canfurther comprise an upper electrode 70 to which RF power can be coupledfrom RF generator 72 through impedance match network 74. A typicalfrequency for the application of RF power to the upper electrode canrange from about 0.1 MHz to about 200 MHz. Additionally, a typicalfrequency for the application of power to the lower electrode can rangefrom about 0.1 MHz to about 100 MHz. Moreover, controller 14 is coupledto RF generator 72 and impedance match network 74 in order to controlthe application of RF power to upper electrode 70. The design andimplementation of an upper electrode is well known to those skilled inthe art.

In the embodiment shown in FIG. 6, the plasma processing system 1 d can,for example, be similar to the embodiments of FIGS. 2 and 3, and canfurther comprise an inductive coil 80 to which RF power is coupled viaRF generator 82 through impedance match network 84. RF power isinductively coupled from inductive coil 80 through dielectric window(not shown) to plasma processing region 45. A typical frequency for theapplication of RF power to the inductive coil 80 can range from about 10MHz to about 100 MHz. Similarly, a typical frequency for the applicationof power to the chuck electrode can range from about 0.1 MHz to about100 MHz. In addition, a slotted Faraday shield (not shown) can beemployed to reduce capacitive coupling between the inductive coil 80 andplasma. Moreover, controller 14 is coupled to RF generator 82 andimpedance match network 84 in order to control the application of powerto inductive coil 80. In an alternate embodiment, inductive coil 80 canbe a “spiral” coil or “pancake” coil in communication with the plasmaprocessing region 15 from above as in a transformer coupled plasma (TCP)reactor. The design and implementation of an inductively coupled plasma(ICP) source, or transformer coupled plasma (TCP) source, is well knownto those skilled in the art.

Alternately, the plasma can be formed using electron cyclotron resonance(ECR). In yet another embodiment, the plasma is formed from thelaunching of a Helicon wave. In yet another embodiment, the plasma isformed from a propagating surface wave. Each plasma source describedabove is well known to those skilled in the art.

In the following discussion, a method of etching an organic ARC layerutilizing a plasma processing device is presented. For example, theplasma processing device can comprise various elements, such asdescribed in FIGS. 2 through 6, and combinations thereof.

In one embodiment, the method of etching an organic ARC layer comprisesan NH₃/O₂ based chemistry. For example, a process parameter space cancomprise a chamber pressure of about 20 to about 1000 mTorr, an NH₃process gas flow rate ranging from about 50 to about 1000 sccm, an O₂process gas flow rate ranging from about 5 to about 100 sccm, an upperelectrode (e.g., element 70 in FIG. 5) RF bias ranging from about 500 toabout 2000 W, and a lower electrode (e.g., element 20 in FIG. 5) RF biasranging from about 10 to about 500 W. Also, the upper electrode biasfrequency can range from about 0.1 MHz to about 200 MHz, e.g., 60 MHz.In addition, the lower electrode bias frequency can range from about 0.1MHz to about 100 MHz, e.g., 2 MHz.

In a first example, a method of etching an organic ARC layer utilizing aplasma processing device such as the one described in FIG. 5 ispresented. However, the methods discussed are not to be limited in scopeby this exemplary presentation. Table I presents the critical dimensionsof a feature etched in an organic ARC layer utilizing the followingexemplary process recipe: Chamber pressure=100 mTorr; Upper electrode RFpower=1200 W; Lower electrode RF power=100 W; Process gas flow rateNH₃/O₂=360/36 sccm; a 60 mm electrode spacing between the lower surfaceof electrode 70 (see FIG. 5) and the upper surface of substrate 25 onsubstrate holder 20; Lower electrode temperature (e.g., substrate holder20 in FIG. 5)=20 C; Upper electrode temperature (e.g., electrode 70 inFIG. 5)=60 C; Chamber wall temperature=50 C; Backside helium pressureCenter/Edge=10/35 Torr; and an etch time of 184 seconds (equivalent to a20% over-etch from the detection of endpoint using, for example,diagnostic system 12).

TABLE I NH₃/O₂ CENTER EDGE Top PR Remaining 155 nm 164 nm Top CD 212 nm202 nm Bottom CD 200 nm 286 nm CD bias  +1 nm  +0 nm

In Table I and the following Tables, PR refers to photoresist and CDrefers to critical dimension. The Table reports results such asthickness of the remaining photoresist following the ARC layer etch, topand bottom critical dimensions for the ARC feature, and the criticaldimension bias. Additionally, the data is reported at center and edge.The data demonstrates the success of the process in maintaining the CD.

In an alternate embodiment, the process chemistry can further compriseHelium (He). The introduction of Helium to the process can relievefeature side-wall roughness.

In a second example, Table II presents the critical dimensions of afeature etched in an organic ARC layer utilizing the following exemplaryprocess recipe: Chamber pressure=100 mTorr; Upper electrode RFpower=1200 W; Lower electrode RF power=100 W; Process gas flow rateNH₃/O₂/He=360/36/100 sccm; a 60 mm electrode spacing between the lowersurface of electrode 70 (see FIG. 5) and the upper surface of substrate25 on substrate holder 20; Lower electrode temperature (e.g., substrateholder 20 in FIG. 5)=20 C; Upper electrode temperature (e.g. electrode70 in FIG. 5)=60 C; Chamber wall temperature=50 C; Backside heliumpressure Center/Edge=10/35 Torr; and an etch time of 168 seconds(equivalent to a 18% over-etch from the detection of endpoint using, forexample, diagnostic system 12).

NH₃/O₂/He CENTER EDGE Top PR Remaining 168 nm 171 nm Top CD 213 nm 208nm Bottom CD 202 nm 201 nm CD bias  +7 nm  +6 nmTable II

Table II reports results such as thickness of the remaining photoresistfollowing the ARC layer etch, top and bottom critical dimensions for theARC feature, and the critical dimension bias. Additionally, the data isreported at center and edge. The data demonstrates the success of theprocess. Furthermore, the process associated with Table II reportssimilar results to that reported in Table I. However, SEM data indicatesthat the addition of He tends to relieve feature side-wall roughness(not shown) with a minor loss in CD.

In an alternate embodiment, the method of etching an organic ARC layercan comprise an N₂/H₂/O₂ based chemistry. The process parameter spacecan comprise a chamber pressure of about 20 to about 1000 mTorr, an N₂process gas flow rate ranging from about 50 to about 1000 sccm, an H₂process gas flow rate ranging from about 50 to about 1000 sccm, an O₂process gas flow rate ranging from about 5 to about 100 sccm, an upperelectrode (e.g., element 70 in FIG. 5) RF bias ranging from about 500 toabout 2000 W, and a lower electrode (e.g., element 20 in FIG. 5) RF biasranging from about 10 to about 500 W.

In a third example, a method of etching an organic ARC layer utilizing aplasma processing device such as the one described in FIG. 5 ispresented. However, the methods discussed are not to be limited in scopeby this exemplary presentation. Table III presents the criticaldimensions of a feature etched in an organic ARC layer utilizing thefollowing process recipe: Chamber pressure=100 mTorr; Upper electrode RFpower=1200 W; Lower electrode RF power=100 W; Process gas flow rateN₂/H₂/O₂=100/300/36 sccm; a 60 mm electrode spacing between the lowersurface of electrode 70 (see FIG. 5) and the upper surface of substrate25 on substrate holder 20; Lower electrode temperature (e.g., substrateholder 20 in FIG. 5)=20 C; Upper electrode temperature (e.g., electrode70 in FIG. 5)=60 C; Chamber wall temperature=50 C; Backside heliumpressure Center/Edge=10/35 Torr; and an etch time of 150 seconds(equivalent to a 21% over-etch from the detection of endpoint using, forexample, diagnostic system 12).

TABLE III N₂/H₂/O₂ CENTER EDGE Top PR Remaining 177 nm 163 nm Top CD 273nm 295 nm Bottom CD 289 nm 295 nm CD bias  94 nm 100 nm

Table III also demonstrates the success of the method.

In an alternate embodiment, the N₂/H₂/O₂ process chemistry can furthercomprise Helium (He). The introduction of Helium to the process canrelieve feature side-wall roughness.

In an alternate embodiment, the method of etching an organic ARC layercomprises an NH₃/CO or NH_(3/)CO/O₂ based chemistry. The process gas mayalso include helium. For example, a process parameter space can comprisea chamber pressure of about 20 to about 1000 mTorr, an NH₃ process gasflow rate ranging from about 50 to about 1000 sccm, and a CO process gasflow rate ranging from about 5 to about 300 sccm. When O₂ is included inthe process gas, it can have a flow rate in the range of about 5 toabout 100 sccm. When He is included in the process gas of this or any ofthe embodiments of this application, it can have a flow rate in therange of about 5 to about 300 sccm. An upper electrode (e.g., element 70in FIG. 5) RF bias can range from about 500 to about 2000 W, a lowerelectrode (e.g., element 20 in FIG. 5) RF bias can rang from about 10 toabout 500 W, the upper electrode bias frequency can range from about 0.1MHz to about 200 MHz, e.g., 60 MHz, and the lower electrode biasfrequency can range from about 0.1 MHz to about 100 MHz, e.g., 2 MHz.

In a fourth example, a method of etching an organic ARC layer utilizinga plasma processing device such as the one described in FIG. 5 ispresented. However, the methods discussed are not to be limited in scopeby this exemplary presentation. Table IV presents the criticaldimensions of a feature etched in an organic ARC layer utilizing thefollowing exemplary process recipe: Chamber pressure=200 mTorr; Upperelectrode RF power=1200 W; Lower electrode RF power=200 W; Process gasflow rate NH₃/CO=300/100 sccm; a 60 mm electrode spacing between thelower surface of electrode 70 (see FIG. 5) and the upper surface ofsubstrate 25 on substrate holder 20; Lower electrode temperature (e.g.,substrate holder 20 in FIG. 5)=20 C; Upper electrode temperature (e.g.,electrode 70 in FIG. 5)=60 C; Chamber wall temperature=50 C; Backsidehelium pressure Center/Edge=10/35 Torr; and an etch time of 180 seconds.

TABLE IV NH₃/CO ISOLATED NESTED IL Thickness  68 nm  68 nm PR Depth 598nm 589 nm Bottom CD 161 nm 154 nm CD bias  −2 nm −10 nm

In Table IV, IL thickness refers to the thickness of the upper layer ofthe bilayer mask (i.e., the thickness of the light-sensitive layer 3 inFIGS. 1A-C), PR depth refers to the thickness of the lower layer of thebilayer mask (i.e., the thickness of the anti-reflective coating (ARC)layer 7), Bottom CD refers to the critical dimension at the featurebottom following the transfer of the pattern in the light-sensitive,upper layer to the lower ARC layer via etching, and CD bias refers tothe difference between the critical dimension at the feature bottom inthe light-sensitive layer prior to etching the ARC layer and thecritical dimension at the feature bottom in the ARC layer followingetching the ARC layer. Additionally, the data is reported for bothisolated features (i.e., broad spacing of features) and nested features(i.e., close spacing of features). The data demonstrates the success ofthe process in maintaining the CD, particularly, for feature aspectratios greater than or equal to about 3-to-1 or greater than or equal toabout 4-to-1.

In a fifth example, a method of etching an organic ARC layer utilizing aplasma processing device such as the one described in FIG. 5 ispresented. However, the methods discussed are not to be limited in scopeby this exemplary presentation. Table V presents the critical dimensionsof a feature etched in an organic ARC layer utilizing the followingexemplary process recipe: Chamber pressure=200 mTorr; Upper electrode RFpower=1200 W; Lower electrode RF power=200 W; Process gas flow rateNH₃/CO=250/150 sccm; a 60 mm electrode spacing between the lower surfaceof electrode 70 (see FIG. 5) and the upper surface of substrate 25 onsubstrate holder 20; Lower electrode temperature (e.g., substrate holder20 in FIG. 5)=20 C; Upper electrode temperature (e.g., electrode 70 inFIG. 5)=60 C; Chamber wall temperature=50 C; Backside helium pressureCenter/Edge=10/35 Torr; and an etch time of 240 seconds.

TABLE V NH₃/CO ISOLATED NESTED IL Thickness  93 nm 100 nm PR Depth 696nm 643 nm Bottom CD 171 nm 171 nm CD bias  7 nm  6 nm

In Table V, IL thickness refers to the thickness of the upper layer ofthe bilayer mask (i.e., the thickness of the light-sensitive layer 3 inFIGS. 1A-C), PR depth refers to the thickness of the lower layer of thebilayer mask (i.e., the thickness of the anti-reflective coating (ARC)layer 7), Bottom CD refers to the critical dimension at the featurebottom following the transfer of the pattern in the light-sensitive,upper layer to the lower ARC layer via etching, and CD bias refers tothe difference between the critical dimension at the feature bottom inthe light-sensitive layer prior to etching the ARC layer and thecritical dimension at the feature bottom in the ARC layer followingetching the ARC layer. Additionally, the data is reported for bothisolated features (i.e., broad spacing of features) and nested features(i.e., close spacing of features). The data further demonstrates thesuccess of the process in maintaining the CD, particularly, for featureaspect ratios in excess of 4.5-to-1.

In a sixth example, a method of etching an organic ARC layer utilizing aplasma processing device such as the one described in FIG. 4 ispresented. However, the methods discussed are not to be limited in scopeby this exemplary presentation. Table VI presents the criticaldimensions of a feature etched in an organic ARC layer utilizing thefollowing exemplary process recipe: Chamber pressure=100 mTorr; Lowerelectrode RF power=300 W; Process gas flow rate NH₃/O₂/CO=200/10/50sccm; a 47 mm electrode spacing between the lower surface of the upperwall of chamber 10 (see FIG. 4) and the upper surface of substrate 25 onsubstrate holder 20; Lower electrode temperature (e.g., substrate holder20 in FIG. 4)=40 C; Upper wall of chamber 10 temperature=60 C; Chamberwall temperature=40 C; Backside helium pressure Center/Edge=10/40 Torr;and an etch time of 140 seconds (includes 15% over-etch).

TABLE VI 1:5 1:3 1:1.5 NH₃ w/OE Bottom CD C/E 158/158 nm 156/158 nm162/155 nm CD bias C/E  −5/−5 nm  −3/−1 nm  +2/−5 nm Top PR remainingC/E  79/88 nm Top PR loss C/E −71/−62 nm NH₃/O₂ Bottom CD C/E 176/158 nm173/169 nm 178/170 nm CD bias C/E +16/+12 nm +14/+10 nm +16/+10 nm TopPR remaining C/E 96/110 nm Top PR loss C/E −54/−40 nm NH₃/CO/O₂ BottomCD C/E 164/160 nm 164/159 nm 165/159 nm CD bias C/E  +4/−3 nm   +5/0 nm +3/−1 nm Top PR remaining C/E 103/110 nm Top PR loss C/E −47/−40 nm

In Table VI, the results of the above-identified chemistry (i.e.,NH₃/CO/O₂) are presented for three different feature spacings (orpitch), i.e., a feature width-to-spacing of 1:5, 1:3, and 1:1.5. Theresults are presented for substrate center and edge (C/E), whereinBottom CD refers to the critical dimension at the feature bottomfollowing the transfer of the pattern in the light-sensitive, upperlayer to the lower ARC layer via etching, CD bias refers to thedifference between the critical dimension at the feature bottom in thelight-sensitive layer prior to etching the ARC layer and the criticaldimension at the feature bottom in the ARC layer following etching theARC layer, Top PR remaining refers to the thickness of the upper,light-sensitive layer following the etching of the ARC layer, and Top PRloss refers to the thickness of the upper, light-sensitive layer thatremains following etching the ARC layer.

Also shown in Table VI are results for two other chemistries, namely, apure ammonia (NH₃) chemistry with 35% over-etch, and a NH₃/O₂ chemistrywith 15% over-etch. In the former chemistry, the process recipe issimilar to that of the NH₃/CO/O₂ chemistry except for a Lower electrodeRF power=500 W, a Process gas flow rate NH₃=400 sccm (no CO and O₂ flowrate), and an etch time of 90 seconds (includes 35% over-etch).Furthermore, in the latter chemistry, the process recipe is similar tothat of the NH₃/CO/O₂ chemistry except for a Process gas flow rate O₂=20sccm (no CO flow rate), and an etch time of 135 seconds (includes 20%over-etch). As shown in Table VI, the CD bias for the pure ammonia caseis low, which, for example, is desirable; however, significant residueis formed at the bottom of the feature during the etching of the ARClayer. In contrast, when O₂ is added to the process chemistry, theresidue formation at the bottom of the feature is removed; yet, the CDbias is greater. However, when O₂ and CO are added to the processchemistry, the residue formation at the bottom of the feature isremoved, and the CD bias is low (as in the pure ammonia case).

In general, the etch time can be determined using design of experiment(DOE) techniques; however, it can also be determined using endpointdetection. One possible method of endpoint detection is to monitor aportion of the emitted light spectrum from the plasma region thatindicates when a change in plasma chemistry occurs due to substantiallynear completion of the ARC layer etching and contact with the underlyingmaterial film. For example, portions of the spectrum that indicate suchchanges comprise wavelengths of 387.2 nm (CN), and can be measured usingoptical emission spectroscopy (OES). After emission levels correspondingto those frequencies cross a specified threshold (e.g., drop tosubstantially zero or increase above a particular level), an endpointcan be considered to be complete. Other wavelengths that provideendpoint information can also be used. Furthermore, the etch time can beextended to include a period of over-etch, wherein the over-etch periodconstitutes a fraction (i.e. 1 to 100%) of the time between initiationof the etch process and the time associated with endpoint detection.

FIG. 7 presents a flow chart of a method for etching an anti-reflectivecoating (ARC) layer on a substrate in a plasma processing systemaccording to an embodiment of the present invention. Procedure 400begins in 410 in which a process gas is introduced to the plasmaprocessing system, wherein the process gas comprises a nitrogen (N)containing gas, a hydrogen (H) containing gas, and an oxygen (O)containing gas. For example, the process gas can comprise ammonia (NH₃),and diatomic oxygen (O₂). Alternately, the process gas can comprisediatomic nitrogen (N₂), diatomic hydrogen (H₂), and diatomic oxygen(O₂). Alternately, the process gas can comprise ammonia (NH₃), andcarbon monoxide (CO). Alternately, the process gas can comprise ammonia(NH₃), carbon monoxide (CO), and oxygen (O₂). Alternately, the processgas can comprise diatomic nitrogen (N₂), diatomic hydrogen (H₂), andcarbon monoxide (CO). Alternately, the process gas can further comprisehelium (He).

In 420, a plasma is formed in the plasma processing system from theprocess gas using, for example, any one of the systems described inFIGS. 2 through 6, and combinations thereof.

In 430, the substrate comprising the ARC layer is exposed to the plasmaformed in 420. After a first period of time, procedure 400 ends. Forexample, the first period of time during which the substrate with theARC layer is exposed to the plasma is generally dictated by the timerequired to etch the ARC layer, or the time required to transfer aphotoresist pattern to the ARC layer. In general, the first period oftime required to transfer a photoresist pattern through the thickness ofthe ARC layer is pre-determined. Alternately, the first period of timecan be further augmented by a second period of time, or an over-etchtime period. As described above, the over-etch time can comprise afraction of time, such as 1 to 100%, of the first period of time, andthis over-etch period can comprise an extension of etching beyond thedetection of endpoint.

FIG. 8 presents a method for forming a bilayer mask for etching a thinfilm on a substrate in a plasma processing system according to anotherembodiment of the present invention. The method is illustrated in aflowchart 500 beginning in 510 with forming the thin film on thesubstrate. The thin film can comprise an oxide layer, such as silicondioxide (SiO₂), and it can be formed by a variety of processes includingchemical vapor deposition (CVD).

In 520, an anti-reflective coating (ARC) layer is formed on thesubstrate overlying the thin film. The ARC layer can, for example, be anorganic ARC layer that is formed using conventional techniques such as aspin coating system.

In 530, a photoresist pattern is formed on the substrate overlying theARC layer. The photoresist film can be formed using conventionaltechniques, such as a photoresist spin coating system. The pattern canbe formed within the photoresist film by using conventional techniquessuch as a stepping micro-lithography system, and a developing solvent.

In 540, the photoresist pattern is transferred to the ARC layer in orderto form the bilayer mask. The pattern transfer is accomplished using adry etching technique, wherein the etch process is performed in a plasmaprocessing system that utilizes a process gas comprising a nitrogen (N)containing gas, a hydrogen (H) containing gas, and an oxygen (O)containing gas. For example, the process gas can comprise ammonia (NH₃),and diatomic oxygen (O₂). Alternately, the process gas can comprisediatomic nitrogen (N₂), diatomic hydrogen (H₂), and diatomic oxygen(O₂). Alternately, the process gas can comprise ammonia (NH₃), andcarbon monoxide (CO). Alternately, the process gas can comprise ammonia(NH₃), carbon monoxide (CO), and oxygen (O₂). Alternately, the processgas can comprise diatomic nitrogen (N₂), diatomic hydrogen (H₂), anddiatomic oxygen (O₂). Alternately, the process gas, as described above,can further comprise helium (He). Plasma is formed in the plasmaprocessing system from the process gas using, for example, any one ofthe systems described in FIGS. 2 through 6, and the substrate comprisingthe ARC layer is exposed to the plasma formed. A first period of timeduring which the substrate with the ARC layer is exposed to the plasmais generally dictated by the time required to etch the ARC layer, or thetime required to transfer a photoresist pattern to the ARC layer. Ingeneral, the first period of time required to transfer a photoresistpattern through the thickness of the ARC layer is pre-determined.However, typically, the first period of time is further augmented by asecond period of time, or an over-etch time period. As described above,the over-etch time can comprise a fraction of time, such as 1 to 100%,of the first period of time, and this over-etch period can comprise anextension of etching beyond the detection of endpoint.

Although only certain embodiments of this invention have been describedin detail above, those skilled in the art will readily appreciate thatmany modifications are possible in the embodiments without materiallydeparting from the novel teachings and advantages of this invention.Accordingly, all such modifications are intended to be included withinthe scope of this invention.

1. A method for etching an organic-based anti-reflective coating (ARC) layer on a substrate in a plasma processing system comprising: introducing a process gas consisting of N₂, H₂, O₂, CO, and optionally helium, wherein; forming a plasma from said process gas in said plasma processing system; and exposing said substrate with said organic-based ARC layer to said plasma in order to etch said organic-based ARC layer while removing residue formation on said substrate.
 2. The method as recited in claim 1, wherein said exposing said substrate with said organic-based ARC layer to said plasma is performed for a first period of time.
 3. The method as recited in claim 2, wherein said first period of time is determined by endpoint detection.
 4. The method as recited in claim 3, wherein said endpoint detection comprises optical emission spectroscopy.
 5. The method as recited in claim 2, wherein said first period of time corresponds to the time to etch said organic-based ARC layer and is extended by a second period of time.
 6. The method as recited in claim 5, wherein said second period of time is a fraction of said first period of time.
 7. A method for etching a feature in an organic-based anti-reflective coating (ARC) layer on a substrate in a plasma processing system comprising: introducing a process gas consisting of ammonia (NH₃), carbon monoxide (CO), oxygen (O₂), and optionally helium; forming a plasma from said process gas is said plasma processing system; and exposing said substrate with said organic-based ARC layer to said plasma in order to etch said organic-based ARC layer while removing residue formation on said substrate.
 8. The method as recited in claim 7, wherein the flow rate of NH₃ is in the range of about 50 to about 1000 sccm, the flow rate of O₂ is in the range of about 5 to about 100 sccm and the flow rate of CO is in the range of about 5 to about 300 sccm.
 9. The method as recited in claim 7, wherein the flow rate of helium is in the range of about 5 to about 300 sccm.
 10. The method as recited in claim 7, wherein said exposing said substrate with said organic-based ARC layer to said plasma is performed for a first period of time.
 11. The method as recited in claim 10, wherein said first period of time is determined by endpoint detection.
 12. The method as recited in claim 11, wherein said endpoint detection comprises optical emission spectroscopy.
 13. The method as recited in claim 10, wherein said first period of time corresponds to the time to etch said organic-based ARC layer and is extended by a second period of time.
 14. The method as recited in claim 13, wherein said second period of time is a fraction of said first period of time. 